* tests/test-vprintf-gnu.sh: New file, based on
tests/test-vprintf-posix.sh.
* tests/test-vprintf-gnu.c: New file, based on
tests/test-vprintf-posix.c.
* tests/test-printf-gnu.h: New file, based on
tests/test-vasnprintf-gnu.c.
* modules/vprintf-gnu-tests: New file, based on
modules/vprintf-posix-tests.
